1. Field of the Invention
This invention relates to new polyamide resins and to their use as hotmelt adhesives. In addition to dimerized fatty acids in the acid portion of the molecule, the polyamide resins of this invention are produced using aliphatic diamines capable of diamide formation which are alkyl-substituted on at least one nitrogen atom.
2. Description of Related Art
Hotmelt adhesives are becoming increasingly important in the adhesives field. These adhesives are advantageous since they achieve necessary bond strength by cooling from the melt and, as such, are suitable for high-speed production operations. A further advantage resides in the fact that the use of equipment to protect against solvent vapors is unnecessary. Moreover, the prolonged drying times needed when aqueous adhesives are used, are substantially shortened when hotmelts are used.
An important class of hotmelts are the polyamides. Of these, polyamides based on dimerized fatty acids have acquired particular significance. Among the polyamides based on dimerized fatty acids, those containing dimerized fatty acids in the acid component and ether diamines in the amine component are particularly important as a result of their favorable low-temperature properties.
Thus, for example, German Application No. 27 54 233 describes copolyamide resins which contain in the acid portion of the molecule a special mixture of polymeric fatty acids (dimer fatty acid) and aliphatic dicarboxylic acids containing from 6 to 12 carbon atoms and, on the base side, a mixture of saturated aliphatic diamines and polyoxyalkylene diamines. These products have an embrittlement temperature of -25.degree. C.
Similar resins are described in U.S. Pat. No. 4,218,351 which relates to polyamides containing, in addition to the usual raw materials, from 5 to 30 mole percent dimer fatty acid and from 0.25 to 12.5 mole percent amorphous oligomers (polyoxyalkylene diamines).
Although the polyetherdiamine-containing polyamides discussed above are adequate for many applications, a need continues to exist to improve substrate adhesion while at the same time retaining, or improving, low-temperature behavior. There is also a need for products having a lower water uptake capacity.